1. Field of the Invention
The present invention relates to a battery pack made up of two or more prismatic batteries electrically connected together.
2. Description of the Related Art
Battery assembly, more commonly known as a “battery module” or “battery pack”, is made up of two or more batteries that are connected in series to output a predetermined voltage, and used for the power source of cordless devices such as mobile phones and electric tools, or of hybrid vehicles. With the downsizing of electric devices, volume-efficient prismatic batteries are increasingly used. One problem with the battery pack of prismatic batteries is that because the batteries are arranged in face-to-face relationship, the terminals of adjacent batteries that are to be connected are located more closely to each other as compared to a battery pack of cylindrical batteries, and also the connectors for connecting these terminals are smaller than those used for cylindrical batteries, because of which precise positioning of terminals and connectors relative to each other is hard to achieve.
When connecting two prismatic batteries, the connector is held by a jig or human fingers, and its position is adjusted relative to the cap-like terminal of the prismatic battery. It is difficult, however, to ensure that the small connector is always precisely positioned in a reliable manner, and because of this difficulty in positioning of the components, the work efficiency of spot welding is extremely poor. Also, there is always the risk of weld failure caused by a misaligned connector and of other troubles such as short-circuiting caused by a dropped connector.
In light of these problems, the applicant of the present invention has proposed a design that facilitates series connection of prismatic batteries of a battery pack, with which connectors are precisely positioned in a reliable manner on the cap-like terminals of the batteries before the welding, and the risk of weld failure caused by misalignment of the connector during the spot-welding is reduced (Japanese Patent Laid-Open Publication No. Hei 11-167912).
FIG. 5 and FIG. 6 show this type of battery pack: Prismatic batteries Ba1 shown in FIG. 6 are connected together using a connector 30 shown in FIG. 5. The connector 30 consists of a flat end 30a to be welded to the electrode terminal plate 32 of one prismatic battery Ba1, and a square U-shaped slit with a pair of engaging ends 30b and 30c formed by bending. The engaging ends are fitted onto the cap-like terminal 31 of the other prismatic battery Ba1 such as to cover the terminal from both sides.
When connecting two batteries Ba1 with this connector 30, the pair of engaging ends 30b and 30c are placed over the cap-like terminal 31 so that the connector 30 is set in position in both widthwise and lengthwise directions relative to the battery Ba1. The position of the connector 30 is thus defined reliably and the risk of weld failure resulting from misalignment of the connector during the spot welding is reduced. Moreover, when fitted onto the cap-like terminal 31, the connector 30 need not be held with fingers or the like, which largely reduces the time required for the positioning during welding.
On the other hand, when arranging the batteries face to face so that the positive electrode and the negative electrode of two adjacent batteries Ba1 are in alternate positions, they must be positioned relative to each other with an offset x in the height direction that corresponds to the height of the cap-like electrode terminal 31. Thus, if there is a variation in the height of the cap-like electrode terminal 31 and flat electrode terminal 32 of the batteries Ba1, the contact between the connector 30 and the terminals 31 and 32 may not be tight enough, leading to a weld failure in which the connector 30 separates from the terminal 31 or 32 by vibration or the like.
Another problem is that the above-described connector 30 cannot be used for electrically connecting prismatic batteries Ba2 of the type shown in FIG. 1, which each have a negative terminal 3 protruding from the sealing plate 2 that closes one open end of the battery case 1.